1. Field of the Invention
The present invention relates to a paper sheet feeder, and more particularly to a paper sheet feeder which can feed sheets of paper from any one of several paper cassettes as desired, to an image-forming unit incorporated in an image forming apparatus such as an electronic copying machine.
2. Description of the Related Art
Recently, a variety of image forming apparatuses have been put to practical use, each of which has an image forming unit and a paper sheet feeder. As disclosed in U.S. Pat. No. 4,639,125, the paper sheet feeder feeds sheets of paper, one by one, from a paper cassette to an image forming unit through a transfer path which comprises a plurality of rollers and guide plates. As disclosed in U.S. Pat. No. 4,605,215, the paper sheet feeder, however, has no means for adjusting the position of each sheet just taken from the cassette, but rather has registration rollers located in front of the image-forming unit. The registration rollers adjust the position of the sheet as immediately as the sheet is fed to the image-forming unit.
The conventional paper sheet feeder described above, designed for use in an image forming apparatus having a plurality of paper cassettes, has a long transfer path. As is known in the art, a paper sheet often has a skew or is set off the center immediately after it is fed from a paper cassette. Since the transfer path is relatively long, there is a great possibility that such a skew or such an offset increases as the sheet is fed through the path. In the worst case, the skew or setoff increases so much that the sheet can no longer registered at the image-forming unit. If the sheet having skew or set off the center undergoes image-forming process in the image-forming unit, the image formed on the sheet will be slanted one, or only part of the original image will be made.